mohammadjavad sohrabi

Effect of continuous heating after cold deformation on the microstructural evolutions and corrosion behavior of SUS 304L metastable austenitic stainless steel was investigated. After cold rolling with the reduction in thickness of 80%, a microstructure consisting of elongated grains was obtained, in which the X-ray diffraction (XRD) analysis revealed the formation of 96 vol.% strain-induced martensite. The subsequent continuous heating up to 750 °C led to full reversion/recrystallization and the development of an ultrafine grained (UFG) microstructure with an average grain size of 0.45 µm. Continuous heating up to higher temperatures resulted in a significant grain growth, where the average grain size of samples that heated up to 850, 900, 950, and 1100 °C were obtained as 2.5 µm, 5.5 µm, 14 µm, and 45 µm, respectively. The Hall-Patch relationship of H = 155 + 106/√D was developed for the dependence of hardness on the average grain size (D). By grain refinement, corrosion current density (iCorr) increased leading to the worsening of uniform corrosion resistance. However, breakdown potential (EBr) increased by grain refinement, indicating the improved pitting resistance. The Hall-patch-type equations of iCorr = 0.0147 + 0.4458/√D and EBr = 0.1964 + 0.0695/√D were proposed for correlating the corrosion parameters to D.

Deformation-induced α΄-martensite generally forms at shear bands in the coarse-grained austenite, while it nucleates at grain boundaries in the ultrafine-grained (UFG) austenite. The available kinetics models are related to the nucleation on the shear band intersections, and hence, their application to investigating the kinetics of α΄-martensite formation for the UFG regime cannot be justified. Accordingly, in the present work, the general Johnson–Mehl–Avrami–Kolmogorov (JMAK-type) model was implemented for comparing the kinetics of α΄-martensite formation in the UFG and coarse-grained regimes using an AISI 304L stainless steel. On the experimental front, the X-ray diffraction (XRD) patterns and the electron backscattered diffraction (EBSD) maps were used for phase and microstructural analyses, respectively. It was revealed that the simple JMAK-type model, by considering the dependency of the volume fraction of α΄-martensite on the strain, is useful for modeling the experimental data, predicting the nucleation sites based on the theoretical Avrami exponents, and characterizing the transformation kinetics at low and high strains.

Hall-Petch analysis and the effect of the average grain size (D) on the hardness (H) of AISI 309Si stainless steel should be systematically investigated. This aim was achieved by cold rolling (reduction of thickness of 90%) followed by annealing at 1000 °C for different holding times. Cold rolling led to the formation of deformation-induced α΄-martensite and work-hardening of the retained austenite, which led to an increased hardness of 427 HV compared to the hardness of 115 HV for the as-received sample. X-ray diffraction (XRD) analysis revealed the formation of ~30 vol% martensite, which signifies the higher mechanical stability of austenite in this alloy when compared to the metastable grades. At the annealing temperature of 1000 °C, the material is fully austenitic without any intermetallics. Moreover, by occurrence of martensite reversion, recrystallization of the retained austenite, and subsequent grain growth, it is easy to obtain different grain sizes at this temperature. Annealing at 1000 °C for 30 min resulted in a significant increment of hardness (155.1 HV) compared to the as-received sample as well as the formation of a fine-grained microstructure with an average grain size of 6.7 µm, which is equivalent to ~93% refinement of the grain size. Longer annealing times led to the occurrence of grain growth with the resulting decrement of hardness, where D–D0=2.1762×1011exp(–280000/RT)×t0.5 was proposed to predict the grain size during grain coarsening. Moreover, the Hall–Petch relationship of H=140.1/√D+100.7 was proposed for the first time, in which the H0 value of 100.7 HV was also compared to those determined for AISI 316L (130.0 HV) and 304L (160.4 HV) alloys. Furthermore, it was revealed that the increased metastability leads to an increment in the H0 value, which can be correlated with the Md30/50 temperature.

Having a predictive mathematical model regarding the sales potential of movies before the marketing and screening of movies is one of the needs of many producers, Cinema owners, etc. In this research, based on a systematic process and mixed exploratory approach, first the factors affecting the sales potential of movies were calculated and classified by content analysis method and by selecting the content factors of the film, i.e., the factors affecting the probability of pre-marketing and screening; The status of each of these factors in the top 100 films of a decade of Iranian cinema was examined. The required data were extracted from the statistical yearbook of Iranian film and cinema sales and based on Shannon entropy method and based on real data of 100 popular Iranian films, model coefficients were extracted and finally, a mathematical model to calculate the sales potential of a film up to Extracted before the marketing phase. The results of this study indicate that the 4 main factors of director (with coefficient of 0.25), actor (with coefficient of 0.253), genre (with coefficient of 0.251) and technical quality of film (with coefficient of 0.246) and a sub-factor of film series (with extra score) affect the sales potential of a movie.

The notable contributions of Iranian scientists in the field of formation and reversion of strain-induced martensite for grain refinement and enhanced mechanical properties of Fe-Cr-Ni austenitic stainless steels are reviewed. Accordingly, the processing of ultrafine grained (UFG) structure via cold rolling and reversion annealing is summarized for AISI 301, 304, 309Si, 316, and 321 stainless steels, as well as their variants. The repetitive and innovative thermomechanical processing routes are introduced as well. The understanding of the stages of annealing (reversion of strain-induced martensite to austenite, primary recrystallization of the retained austenite, and grain growth) and the underlying reversion mechanisms (diffusional-type and martensitic shear-type) constitute the subsequent part of this overview. Finally, the transformation-induced plasticity (TRIP) effect in the reversion-treated metastable austenitic stainless steels is discussed. The present review paper summarizes these achievements with the discussion on the future prospects in this research field.

The microstructure of Inconel 718 superalloy in the as-cast (vacuum arc remelted and cast in a water-cooled copper mold) and homogenized conditions was studied. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used for microstructural studies and elemental analysis, respectively. The presence of austenite/Laves eutectic constituent and carbides was discussed based on the phase diagram and the microsegregation of niobium and molybdenum between dendrite arms of the austenite matrix. In the eutectic structure, the amount of Nb was estimated to be ~ 20 wt%, which is much higher than the corresponding value of ~ 5 wt% in the original chemical composition of the alloy. Based on the elemental analysis, the Laves phase and carbides were characterized as Ni2Nb and MC, respectively. The dissolution of the Laves phase and the disappearance of the dendritic structure as a result of the elevated temperatures homogenization were also studied and it was revealed that the carbide particles remain in the microstructure after homogenization.

Since the diffusion of alloying elements in nickel has been studied based on the diffusion couples and the presence of other alloying elements can alter the diffusion of a given element, there is need for a method for direct calculation of the diffusivities form the superalloys. In the present work, the as-cast microstructure of Inconel 718 superalloy was studied, where this microstructure was composed of austenitic dendrites that rejected alloying elements such as Nb, Mo, and Ti to the interdendritic regions. Moreover, the Laves phase/austenite eutectic structure and NbC and TiC phases were characterized in the interdendritic regions. Subsequently, the microsegregation of Nb, Mo, and Ti in the as-cast ingot and its amendment during homogenization heat treatment was studied. Based on the concept of residual segregation index, during homogenization treatment, the diffusivities and the corresponding activation energies for diffusion of these elements in the austenitic matrix were obtained. The activation energy for the interdiffusion of Nb, Mo, and Ti was determined as 232, 286, and 256 kJ/mol, respectively. The outcome of these calculations is important for the precipitation reactions, high-temperature creep, and thermomechanical processing of superalloys.